A centralized radio access network (C-RAN) including a baseband unit (BBU) and a remote radio head (RRH) has recently been studied for the realization of the fifth generation mobile communication system (5G). As for a mobile front haul (MFH) line between the BBU and the RRH, there has been studied the adoption of a common public radio interface (CPRI) method for transmitting radio analog signals almost without any change.
In a communication system connected to the MFH line, information is handled as layer 2 packets. Therefore, a network is shared with a mobile back haul (MBH) line, a wired network, or the line that connects between the base stations. However, in the communication system, output delay occurs when MFH packets from the MFH line compete with other packets, for example, MBH packets from the MBH line. Therefore, priority control processing for suppressing such output delay is demanded. In the priority control processing, subsequent high-priority packets are preferentially read before queued low-priority packets. Thus, output delay of the high-priority packets, that is, the MFH packets may be suppressed.
However, in the priority control processing, when the high-priority packets arrive during read of the low-priority packets, the read operation of the high-priority packets is stopped until the read output of the low-priority packets being read is completed. As a result, wait of up to about 1 packet occurs. When a link rate is 1 Gbps and a packet length is 9000 bytes, for example, output delay of about 7 μ seconds occurs. In the MFH line, output delay is desirably 100 μ seconds or less between the RRH and the BBU. Therefore, in the case of a multimode configuration, this 1 packet output delay may not be ignored.
Time sensitive networking (TSN) of the institute of electrical and electronics engineers (IEEE) 802.1 has been studied as another method for suppressing the output delay. The TSN includes a time aware shaper (TAS) method of the IEEE 802.1 Qbv as a data plane function to suppress packet output delay. As the related art, Japanese Laid-open Patent Publication No. 2001-177660 and the like are disclosed, for example.
For example, a communication system is assumed, including a plurality of packet switches adopting the TAS method. In this case, each of the packet switches has to adjust opening and closing timing of each gate in the entire communication system, considering the transmission timing at the transmission end of MFH packets as high-priority packets as well as transmission delay for each gate of the packet switch so as to preferentially output the MFH packets. In consideration of the above circumstances, it is desirable that output delay of specific packets may be suppressed.